It is known for vehicles, such as automobiles and aircraft, to include an electronic display providing an image of, for example, an instrument cluster for replacing discrete mechanical or electric dials. However, such displays generally provide limited realism because of their inability to produce images at different depths with respect to the display apparatus. In addition to limiting the realism of such displays, the inability to produce images at different depths reduces the visibility or intelligibility of the images. Although stereoscopic and autostereoscopic displays are known and can produce an impression of a three-dimensional image, such displays do not produce an impression of true depth, being unable to reproduce focusing information correctly Further, such displays may have limited freedom of viewing position and may result in user confusion and even eye strain and headaches.
FIG. 1 of the accompanying drawings illustrates a display of the type disclosed in U.S. Pat. No. 4,736,214 for displaying background and foreground images with different image depths. The display comprises a projector 1 for projecting images carried by a projection film 2 with each frame being divided to provide a background image 3 and a foreground image 4. The projector 1 projects these images simultaneously for each frame onto an optical system comprising a rear projection screen 5, mirrors 6 and 7 and a partially transmitting mirror 8. The background and foreground images are projected via different length optical paths in order to produce a motion picture with two depth planes. Although such an apparatus is capable of showing images with different depths to an audience 9, it is of limited application because of its relatively large size and its use of relatively expensive equipment.
FIG. 2 of the accompanying drawings illustrates a display of the type disclosed in WO 9942889, WO 03040820, WO 04001488, WO 04002143 and WO 04008226. This type of display is of dual-panel construction and comprises a backlight 10 overlaid by spatial light modulators 11 and 12. The spatial light modulators 11 and 12 modulate light from the backlight 10 with a pair of images or sequences of images so as to display the images or sequences at different depths. However, such an arrangement has several disadvantages. For example, the spatial light modulators 11 and 12 may have the same regular patterns of black masks which result in the appearance of Moiré fringes, requiring further optical elements 13 in order to reduce the appearance of such fringes. Also, the use of two (or more) spatial light modulators results in very low light transmission so that a very bright backlight 10 is required in order to achieve the necessary or desired image brightness for viewing.
Such an arrangement is “light-subtractive” so that, for example, pixels in the first modulator 11 must be “on” or transmissive in order for pixels in the line of sight in the second modulator 12 to be visible to a viewer. Thus, a light object cannot be shown on a dark background. Also, as light has to pass through the two spaced modulators 11 and 12, parallax effects can occur at image boundaries.
The use of multiple spatial light modulators substantially increases the cost of such a display as compared with conventional displays using single spatial light modulators. In order to increase the number of depth planes, the number of spatial light modulators must be increased and this results in a linear increase in cost, and an experiential decrease in brightness, with the number of depth planes. Further, such an arrangement requires synchronised control of multiple spatial light modulators.
U.S. Pat. No. 2,402,9626 also discloses a multiple panel display of a similar type intended for use in a wagering gaming apparatus.
EP 01059626 and EP 0454423 disclose multiple layer displays having fixed electrode patterns for use in specific applications, such as in watches or in hand-held games. EP 1265097 discloses a display for an automotive instrument cluster comprising a matrix-addressable display overlaid with a patterned display for showing specific vehicle functions. Such displays have the same disadvantages as the multiple panel displays described above and, in addition, are capable of showing only limited images as determined by the electrode patterns.
EP 1093008, JP 0226211, WO 0911255, JP 62235929 and US 22105516 disclose volumetric displays based on multiple layer scattering and polariser-free display panels. Such displays are intended to improve the brightness of the displayed images compared with light-absorbing display panels. However, displays of this type have various disadvantages. For example, a dark state is produced by a non-scattering state so that light is transmitted to the environment. This is undesirable in many applications, such as in automotive displays particularly during night-time driving. Also, such multiple displays are relatively expensive. Further, displays of this type generally have relatively slow switching times and are unsuitable for use throughout wide temperature ranges, for example as may be found in an automotive environment.
FIG. 3 of the accompanying drawings illustrates a known type of time-sequential projection volume display, for example as disclosed in U.S. Pat. No. 4,333,715, US 22163482 and U.S. Pat. No. 4,670,744. The images for the different planes are displayed sequentially by a projector 15 and projected towards a plurality of projection screens 16. The projection screens 16 are of an active type and are enabled one at a time in synchronism with projection by the projector 15 of the image intended to be viewed at the location of the screen. The projection screens 16 are of reflective or scattering type when switched on and are substantially transparent when switched off. However, such a display is of limited use because of the large volume which it requires. Also, such a display is inconvenient because of the need to synchronize activation of the projection screens with the images projected by the projector.
The DaimlerChrysler F500 Mind Car research vehicle shown at the 2003 Tokyo motor show disclosed an instrument cluster which overlaid, by means of a half-silvered mirror, a standard instrument cluster and a liquid crystal display (LCD) panel. However, such an arrangement requires substantial volume in order to accommodate two displays which must be disposed at an angle with respect to each other. Also, as described hereinbefore, the use of multiple displays makes such a system relatively expensive.
FIGS. 4 to 6 of the accompanying drawings illustrate displays of the type disclosed in WO 09810584. The display shown in FIG. 4 comprises a housing 20 containing a beam-combining element in the form of a partially reflective optical element 21. The housing 20 has a viewing aperture 22 and apertures in which are located display devices 23 and 24 for displaying foreground and background images, respectively. The optical paths from a viewer to the display devices 23 and 24 are different so that the device 23 appears at its actual location whereas the device 24 appears behind the device 23 to provide a virtual background image 25.
The display shown in FIG. 5 of the accompanying drawings comprises a single display device 30 divided into relatively large regions for displaying interlaced foreground and background images as illustrated at 31 and 32. Light from each of the foreground elements 31 passes through a partially reflecting mirror 33 and an array of optical expansion elements 34 directly to a viewing region whereas light from each of the background elements 32 is reflected by a mirror 35 and the partially reflecting mirror 33 so as to have a longer light path to the viewing region.
FIG. 6 of the accompanying drawings illustrates another display comprising a projector 40 and a rotating rod 41 on which are mounted first and second projection screens 42 and 43. The projector projects first and second images or sequences of images in synchronism with the screens 42 and 43, respectively, being in front of the projector.
The display illustrated in FIG. 4 has the disadvantages of occupying a relatively large volume and being relatively expensive because of the use of multiple display devices. The display shown in FIG. 5 has the disadvantage that the interlaced sections of the display device 30 are relatively large so that the additional expansion elements 34 are required in order for the image to fill an entire display region. The presence of such elements results in reduced freedom of movement of a viewer because of the f-number of the elements 34. The elements 34 require exact alignment with the regions of the display device 30 and this is inconvenient during manufacture and increases the cost. Two mirror elements are required for each background section of the display device and this increases the size and cost of manufacture. Any aberration in the elements 34 results in image distortion as a viewer moves relative to the display, even if perfect compensation is provided for on-axis viewing.
The display shown in FIG. 6 of the accompany drawings occupies a relatively large volume and requires a mechanical system to provide different image depths. Also, this display has the inconvenience of requiring means for providing synchronization between the rotary position of the mechanical assembly and the projected images.
US 2005/0156813 discloses a display of the type illustrated in FIG. 7 of the accompanying drawings. The display comprises an LCD panel 45 having a portion 46 for displaying a foreground image and a portion 47 for displaying a background image. The panel 45 supplies light modulated with both images having a polarization direction in the plane of FIG. 7 of the accompanying drawings. Light from the portion 46 passes through a reflective polariser 48 to a viewing region of the display.
Light from the portion 47 passes through a retarder 49, which changes the polarization direction of light by 90° so that it is perpendicular to the plane of FIG. 7 of the accompanying drawings. The resulting light is reflected by a mirror 50 towards the reflective polariser 48 such that the reflected light is again reflected by the polariser 48 towards a viewing region.
Although such a display can provide different image depths from a single LCD panel, separate portions of the panel are required to form the two images so that, in order to create a multiple depth image of a given size, a much larger display panel is required. Also, the presence of the mirror 50 greatly restricts the viewing angle of the display. This also limits the orientations of the image planes, which cannot be perpendicular to the viewing direction.